1. Technical Field
The present invention relates to instrumentation for aircraft and more particularly to a method and apparatus for measuring and calibrating turbulence.
2. Description of the Related Art
Air turbulence, most often a nuisance, can at times pose a potentially serious danger to passengers and air crew alike traveling in aircraft. Safety improvements in the past were designed to protect passengers from some of the hazards of in flight turbulence. For example, these safety improvements included the addition of doors on overhead storage bins and the placement of signs on aircraft seat backs warning passengers of the necessity of keeping seat belts fastened at all times, not simply during take off and landing, while seated.
A goal of commercial airline operators is to provide their passengers with as much comfort as possible. This goal includes, when allowable, freedom of movement through the confined space of the aircraft cabin for the use of laboratories, to retrieve items from carry luggage for on board use, etc. It is also desirable to allow the flight attendant crew to move throughout the cabin during certain phases of the flight in order to accomplish various safety related duties as well as passenger comfort activities. Pilots of an aircraft can restrict movement in the cabin of an aircraft of either passengers or both flight attendants and passengers when the pilots deem this movement could involve a risk of injury. This restriction is most often accomplished by the use of lighted signs indicating that seat belts should be fastened and public address announcements. Times during which movement is typically restricted include take-off, landing and at varying thresholds of turbulence intensity.
To avoid turbulence or to predict intensity levels of turbulence that may be encountered, pilots will rely on many sources of information to avoid turbulence or to predict intensity levels of turbulence. These sources of information include, for example, weather forecasts that may depict wide geographical areas of potential turbulence. Knowledge and experience also assist the pilot in recognition of some of the many conditions where a greater risk of turbulence exist. By far the most numerous and reliable inputs that a pilot will employ in determining the most recent location and intensity of in-flight turbulence are reports of turbulence from other aircraft in the vicinity or on similar flight plan routings.
Pilots provide descriptions of turbulent flight conditions in both frequency and intensity. In an attempt to standardize turbulent forecasts, the FAA has chosen a "typical" aircraft type when forecasting the effect of turbulence. The "typical" aircraft used in estimating is a Saab 340 commuter twin. "Light turbulence" causes slight, erratic changes in altitude, and slight strain against seat belts; unsecured objects are displaced slightly and food services in such a situation. In light turbulence, walking is a possibility without difficultly.
"Moderate turbulence" is a turbulence of greater intensity than light turbulence, but the pilot of the aircraft is still in control at all times. Some strain occurs against seat belts and unsecured objects are displaced in moderate turbulence. Food service and walking are difficult in this type of turbulence.
"Serve turbulence" causes large, abrupt altitude excursions. The aircraft is momentality out of control, and large variations in indicated air speed occur during severe turbulence. Occupants are forced violently against seat belts and unsecure objects are thrown about the cabin. Food service and walking are impossible during severe turbulence.
"Extreme turbulence" causes the aircraft to be tossed about violently, and it is virtually impossible to control and may cause structural damage to the aircraft.
The reports of frequency of turbulence includes "occasional turbulence" which occurs less than one third of the time. "intermittent turbulence" occurs one third to two thirds of the time while continuous turbulence is evidence more than two thirds of the time. "Chop" is defined as rhythmic repetitive turbulence of any intensity and/or frequency.
Pilots will provide descriptions of turbulent flight conditions in both frequency and intensity. An example of such a report would be continuous light or occasional moderate turbulence. These reports, however, are subjective in nature, depending on a pilot's observations. Several factors may influence a pilot's interpretation of turbulent flight conditions and therefore cause variables that hinder the description of exact actual conditions. First and foremost are the ambiguities and inherent difficulties in clearly defining intensity levels. For example, slight strain against the seat belt verses strain against that seat belt (light turbulence verses moderate turbulence) poses a wide area of subjective interpretation by different pilots. Second, the experience level of the pilot making the report also is a subjective factor that can influence the pilot's interpretation of intensity and therefore, cause another variable to accurate reporting. A relatively inexperienced pilot, as expected, would often exaggerate intensity of turbulence. An experienced pilot tends to be more accurate in reports although he or she will sometimes understate the severity of turbulence intensity.
Still another variable to reports of turbulence is the type of aircraft from which the report is made. In general, larger and heavier aircraft with higher wing loading will transgress areas of turbulence with less difficulty and less oscillation than smaller and lighter aircraft. This variance often will affect the pilot's interpretation of intensity. For example, what might be interpreted as severe turbulence to a light, single engine aircraft would most probably be perceived as light to a Boeing 747. Therefore, it would be advantageous to have a method and apparatus that provides an accurate indication of turbulence encountered by an aircraft that lessens or illuminates the impact of various inputs that hinder precise reporting of turbulence.